The present invention relates to nonvolatile erasable programmable memories and more specifically, structures and fabrication techniques for a pillar structure memory cell storage element.
Memory and storage is one of the key technology areas that is enabling the growth in the information age. With the rapid growth in the Internet, World Wide Web (WWW), wireless phones, personal digital assistants (PDAs), digital cameras, digital camcorders, digital music players, computers, networks, and more, there is continually a need for better memory and storage technology.
A particular type of memory is nonvolatile memory. A nonvolatile memory retains its memory or stored state even when power is removed. Some types of nonvolatile erasable programmable memories include as Flash, EEPROM, EPROM, MRAM, FRAM, ferroelectric, and magnetic memories. Some nonvolatile storage products include CompactFlash (CF) cards, MultiMedia cards (MMC), secure digital (SD) cards, Flash PC cards (e.g., ATA Flash cards), SmartMedia cards, and memory sticks.
A widely used type of semiconductor memory storage element is the Flash memory cell. Some types of floating gate memory cells include Flash, EEPROM, and EPROM. There are other types of memory cell technologies such as those mentioned above. Floating gate memory cells such as Flash are discussed as merely an example. The discussion in this application would also apply to other memory technologies beyond floating gate technology with the appropriate modifications.
Memory cells are configured or programmed to a desired configured state. In particular, electric charge is placed on or removed from the floating gate of a storage element (such as a Flash memory cell) to put the cell into two or more stored states. One state is a programmed state and another state is an erased state. A storage element can be used to represent at least two binary states, a 0 or a 1. A storage element can also store more than two binary states, such as a 00, 01, 10, or 11. This storage element can store multiple states and may be referred to as a multistate, multilevel, or multibit memory cell or storage element. This allows the manufacture of higher density memories without increasing the number of memory cells since each memory cell can represent more than a single bit. The cell may have more than one programmed state. For example, for a memory cell capable of representing two bits, there will be three programmed states and an erased state, for a total of four different states. For a memory cell capable of representing three bits, there will be seven programmed states and an erased state, for a total of eight different states.
Despite the success of nonvolatile memories, there also continues to be a need to improve the technology. It is desirable to improve the density, performance, speed, durability, and reliability of these memories. It is also desirable to reduce power consumption and reduce the cost per bit of storage. If the memory storage element is smaller (i.e., takes less area on the integrated circuit), this will allow greater numbers of storage elements to be fabricated on a single integrated circuit. This will reduce the cost per megabyte or gigabyte. With lower cost storage devices, these devices will be within the means of more consumers around the world, and consumers will be able to purchase greater numbers of storage devices to store their data including audio, pictures, and video.
As can be appreciated, there is a need to improve nonvolatile storage elements by reducing their size and also improving their performance.